Eulerian modelling of melt solidification impact during fuel–coolant interaction

• The transport quantities dedicated to the fine fragmentation process are proposed.
• The source terms of transport equations are introduced and discussed.
• The approach how to implement the model into the Eulerian MC3D code is proposed.
• The solidification effect on the vapour explosion strength is demonstrated.

Melt droplet solidification is one major phenomenon acting on the mitigation of the strength of vapour explosions in situations related to nuclear safety. The modelling of solidification effects is then an important challenge for the evaluation of fuel–coolant interaction. We present an attempt for modelling the crust that might develop around melt droplets and its effect on the fine fragmentation within an Eulerian formulation of the flow equations, with application to the MC3D code.A physically-based modelling of the melt droplets temperature profile and a fragmentation criterion for partly solidified droplets are presented. The implementation of these models in the specific case of Eulerian modelling of the melt droplet phase is described. Two additional transported model parameters based on the most important droplets features regarding the fuel–coolant interaction behaviour are derived. The first property to transport is the crust stiffness because it enables the correct prediction of the amount of droplets participating in the droplet fragmentation process. The second is related to the energy transfer from the droplet interior to the surface. This enables to improve the surface temperature determination and reflects the history of the droplet cooling. Also the potential effect of solidification on the vapour explosion strength is shown.